The present invention relates to a speed change gearing, and, more particularly, relates to a lubricated friction speed change gearing which transmits rotational power in a speed changing manner by utilizing planetary movement of a plurality of cylindrical rollers interposed between outer and inner races.
Such a friction speed change gearing having the aforementioned basic structure is known, and is practically used in accordance with various particular designs. In some old designs of this gearing, the spider member, which engages the cylindrical rollers mounted between the inner and outer races so as to take out reduced speed rotary power or so as to put in rotary power for its speed to be increased, was formed to have a bearing shaft at the tip end of each of its spider arms, adapted to engage a roller through a hole along its central axis, in a manner similar to the engagement of a bearing structure composed of a bearing shaft and a rotary hub. In this structure, however, when the gearing was operated at high speed, so that the rollers were rotated at even higher speed, a large quantity of heat was generated at the bearing portions, and, since the heat was not effectively dissipated, there was a danger that the bearing portions would undergo heavy wearing and/or burn sticking.
This problem with regard to the rotary contact between the cylindrical rollers and the spider arms is more difficult to solve because the cylindrical rollers are compressed and elastically deformed between the outer and inner races so as to become slightly elliptical, in order to generate traction force, based upon elastic fluid lubrication between the rollers and the inner and outer races, and therefore the cylindrical rollers do not provide any uniformly cylindrical bearing bores for receiving the bearing shaft portions of the spider arms. In order to avoid this problem it has been proposed in Japanese Patent Application No. 49793/73 (Japanese Laid-Open Publication No. 135073/74), one of the inventors of which is one of the inventors of the present invention, to construct a lubricated friction speed change gearing of the type which employs a plurality of cylindrical rollers mounted between inner and outer races and a spider member having spider arms each mounted between each two adjacent rollers so as to come into sliding contact with the outer surfaces of the cylindrical rollers. In this prior proposition the bearing surfaces of the spider member which slidingly contact the outer surfaces of the cylindrical rollers are each formed as a concavely curved surface which generally follows the convexly curved outer surface of the cylindrical roller, in order to provide the well known general slide bearing structure which forms a thin clearance extending along the two co-operating bearing surfaces for maintaining an oil film.
Further, in view of the fact that a lubricated friction speed change gearing of the type herein discussed which employs a plurality of cylindrical rollers mounted between inner and outer races can provide a high transmission efficiency, because the engagement between the cylindrical rollers and the inner and outer races is rolling engagement, which is inherently less subject to friction loss than is sliding engagement, and that in such a lubrication friction speed change gearing the sole sliding engagement, incorporated between the cylindrical rollers and the spider member, has a great influence on the overall transmission efficiency of the device, in order to accomplish further improvement in this regard, in the assignee's U.S. Pat. No. 4,157,668, it has been proposed to construct the spider member to have bearing shoes at its bearing portions where it contacts the rollers, the major portion of each of said shoes being capable of slight displacement relative to the body of said spider member, so as to form a gap capable of changing its shape between said portion of said shoe and the one of said rollers with which said shoe is in contact, so that the lubricant cushion is adapted to a wide range of operating conditions.